We'd need to be a louder voice than them, a more prominent side of the community.
However, it's only the negatives that people remember things by. In the case of gamers, it's the stereotypes of the aggressive guy who yells all the time playing Call of Duty, the morbidly obese nerd with severe acne playing WoW in his mom's basement, the PC gamer who scoffs at any and all consoles because he is much better than everyone else because he is a PC gamer, and so on and so forth.
With all those corrupting what could be a good image, it's a nearly insurmountable task to replace those as the image, as the representation of the culture.